Overall Goals: Current prognostics used in assessing the risk of distant recurrence of breast cancer are not based on an understanding of mechanisms of tumor cell dissemination and metastatic seeding. As a result it is not clear how to improve their use within personalized treatment plans concerning risk of distant recurrence. It is also unclear how to use current prognostic metrics in anti-metastatic drug treatment trials. This PPG proposes to define the mechanisms responsible for tumor cell migration and dissemination to distant sites. We have discovered that tumor associated macrophages pair with tumor cells using a paracrine loop that drives tumor cell dissemination and metastasis. We have developed novel technologies to 1) directly observe the mechanisms of macrophage-dependent tumor cell dissemination in living mice in real time; 2) collect, and expression profile the migratory and disseminating tumor cells and their helper macrophages cells; 3) derive mutant cell lines and mice to test the mechanisms derived from these profiles in vivo and in vitro; and 4) use 1-3 to discover molecular mechanisms of dissemination and seeding of tumor cells. The projects of this PPG which will .address the above goals are: Project 1- Macrophage subtypes in Tumor Progression and Metastasis will identify sub-populations of macrophages involved in progression allowing more specific drug targeting of the macrophage sub-population driving metastasis. Project 2- Macrophage signaling pathways enhancing tumor progression will define signaling molecules that act in CSF-1 R downstream signaling pathways in tumor associated macrophages to effect tumor cell dissemination and metastasis. Project 3- ErbB3 and Intravasation during Metastasis will study additional interaction networks between tumor cells and macrophages which regulate the initiation and maintenance of the paracrine loop that affects patient survival. Project 4- PI 3-Kinase and Metastasis will provide important new insights into GPCR regulation of macrophage-tumor cell interactions. Project 5- Mechanisms of cell dissemination and metastatic seeding will extend the new technologies and findings of the Projects and Cores of this Program Project to human breast tumor cells to investigate mechanisms behind tumor cell stromal cell interactions that contribute to tumor cell dissemination from primary breast tumors. The technology of the scientific cores is unique and innovative allowing analysis of mechanisms of tumor cell dissemination in live mice in real time and their reconstitution in vitro.